Graphical systems which use real-world trip data (such as location data captured by a GPS sensor mounted in an aircraft) as the basis for a three-dimensional recreation of the original trip must deal with potential inaccuracies in the data, especially when depicting near-ground-level maneuvers, such as takeoff and landing. In the real world, these inaccuracies can be easily handled. For example, an altimeter in an aircraft may show an altitude of three meters above ground level when the plane is actually sitting on the runway. Because the pilot can see and feel that he or she is sitting on the ground, however, the pilot can easily reconcile the error and not be adversely affected by it. Alternately, the pilot can communicate with the control tower of the airport to get additional information (such as the current pressure altitude reading at ground level), and use that information to calibrate their altitude instrument appropriately.
Using inaccurate recorded altitude data to represent the aircraft in a virtual environment, however, would result in the aircraft being depicted offset from the ground by at least the amount of the altitude error. In fact, in a virtual recreation, multiple error sources must be resolved, including altitude source errors, terrain model errors, and model referencing errors (that is, errors introduced because the mounting location of the altitude sensor on the real aircraft is offset from the reference point used for the virtual model).
It would be possible for the graphical software system to ask the user to input information to correct inaccurate altitude information during a virtual recreation of the trip, but this is an impractical and limited approach. Depending on the accuracy and predictability of the altitude data source, a user-entered altitude “correction” may reconcile the altitude information and the terrain model in one location, but make the problem worse in a second location. The variability of some altitude sources, such as a GPS sensor, over time can be significant. It may be that a user-entered “correction” may actually reconcile the altitude at the virtual airport location when the aircraft takes off, but compound the problem when the aircraft lands at the exact same location an hour later, due to the variation in the accuracy of the GPS signal.
These types of data collection errors are relatively small and typically do not cause problems when depicting motion significantly above ground level. For example, if the simulation is showing an aircraft flying at an altitude of 5,000 meters, an altitude error of three meters is not noticeable. However, when the simulated vehicle is operating near the ground, a difference of plus or minus three meters can make the difference of rendering the vehicle above or below the terrain.
What is needed in the art, therefore, is a method for automatically reconciling differences between the altitude data and the terrain model when creating a simulation of near-ground activities.